<!DOCTYPE html>
<html lang="zh_CN">
<head>
    <meta charset="UTF-8">
    <title>page</title>
  <style>
      * {
        margin: 0;
      }
      .page {
          display: flex;
          width: 100%;
          height: 600px;
          flex-direction: column;
          justify-content: space-between;
      }
header {

    height: 50px;
    background-color: #ffff00;
}
.cen {
    width: 100%;
    flex: 1;
    background-color: lightskyblue;
}
footer{
    height: 50px;
    background-color:#ff0000;
}
  </style>
</head>
<body>
<div class="page">
<header></header>
<div class="cen"></div>
<footer></footer>
</div>
</body>
</html>
